Electrolytic etching machine



De- 10, 1940; F. J. BRlsLEE ErAL 2,224,667

ELECTROLYTIC ETCHING MACHINE Filed Feb. 14, 1938 Sheets-Sheet 1 l I. 45 2 so 1I 6,1

52 24v 61 495150/2 Lf '2 l9 24 I l l l l li Fig. 2. me

and Psc/Nuo Bmcxaumv Dec. l0, 1940. F J. BRlsLEE El-AL 2,224,667

ELECTROLYTIC ETCHING MACHINE Filed Feb. 14,l 1938 4 SheetS-SheelI A2 24 Fig. 3.

w y rrvE/v Tons FRANC/s .csem Efe/:Lf: and Rial/m40 Buckel/RN Y Dec. 1o, 1940. 6.6168656 ML 2,224,667

ELECTROLYTIC AE'lCX-IING MACHINE Filed Feb. 14, 1938 4 Sheets-Sheet 3 Fig. 7.

86 85 lV111 106 105 05 105 1# Cf if Iff 90 90 if; 100 96 99 2 3 93 l I/ l l l/ 'l f ,f 1 .l 4/ -Lirif 98 f i j 97V f 92 f 1 I y j 87 88 1 i 88 1, g j 103 91 j 5 2 i E l j Patented Dec. 10, 1940 UNITED STATES PATENT OFFICE Blackburn,

Prescot, England, assignors to British Insulated Cables Limited, Prescot, England, a British company Application February 14, 1938, Serial No. 190,406

In Great Britain June 11, 1935 10 Claims.

This invention deals with electrolytic etching of zinc and other metal plates for the production of printing surfaces and for other purposes and this application is a continuation in part of copending application Serial No. 79,265 filed on May 12, 1936, for Electrolytic etching machines. In such processes, the plate to be etched forms the anode and the passage of current through the bath takes metal from the anode and liberates it at the cathode. A principal requirement of electrolytic etching apparatus is that it should produce a uniform eiect on all parts of the plate. It has been found that, under simple conditions, there is a tendency to produce more rapid etching near the edges of a plate than near the centre. There is also the further defect that, in many cases, the etching extends to the back of the plate near the edges. In addition to avoiding defects of the kind indicated, it is also required that the apparatus should be capable of dealing with a large range of sizes of plates. Generally, these plates are flat and rectangular but they vary'both in dimensions and in proportion. It is the object of the present invention to produce an electrolytic etching apparatus which meets the requirements set out above effectively and conveniently.

The invention deals with cases where the cathode is parallel with the anode, i. e. their surfaces are equi-distant. Uniformity of etching is obtained by so placing the eiective surface of the cathode and making it of such dimensions that the edges of at least two sides thereof, when projected on the anode, lie within the corresponding edge thereof, by a distance dependent on the distance by which the anode and cathode are separated. For instance, with flat anode and cathode spaced apart vertically by a distance Vof from two and a half to three inches,.it is found 4 that satisfactory results are obtained if each edge of the cathode lies within the corresponding edge of the anode by a distance of three quarters to one inch. This distance is found to be constant over a large range of sizes and proportions .45 of plates and to be of the order of one quarter 55 eiect on the finished plate. More frequent turnlarge range of sizes of anodes, it is preferred to luse a large cathode plate and to obtain the re- -quired change of dimensions on one or more sides of the plate by means of movable masks or bar- 10 riers which can be advanced to diierent distances over the plate from an edge or edges thereof so as to leave an uncovered part of the required dimensions. The required masking effect on the other sides of the cathode plate is 15 preferably obtained by the provision of fixed masks covering one or more edges of the cathode plate or by so placing and dimensioning the cathode plate that if its area were projected on the anode plate, one or more of the edges of the 20 area so projected vwould lie inside the boundariesof the anode plate by the required amount.

In the 'following paragraphs, some practical embodiments of the several methods of attaining the object of the invention will be described 25 with the aid of the accompanying drawings.

These drawings show electrolytic'etching machines arranged for the etching of flat plates.

Figure 1 is a longitudinal section of one form of machine and Figure 2 is a transverse section 30 on thevlines II-II of Figure 1. Figures 3 and 4 show respectively in plan and longitudinal section an alternative arrangement of barriers applicable to Figures 1 and 2, Figure 4 being a section on the line`IV-IV of AFigure 3. Figure 5 shows a 35 longitudinal section of a second form of machine on line V--V of Figure 6 and Figure 6 shows a transverse section on the line VI-VI of 'Figure 5. Figure 'I shows alongitudinal section of a third form of machine on the line VII-LVII of Figure '40 8. Figure 8 shows a transverse section on the line v VIII-VIII of Figure 7, and Figure 9 shows a plan view of the said third form of machine.

In all these examples illustrated there are the common features of a tank I which is about two-thirds full of electrolyte up to the line 2 and has supports for the plate to be etched arranged so as to hold it just below the surface of the electrolyte.

Where the plate 3`which is being etched is of zinc it is preferable to make the cathode of zinc.

` All other parts which are immersed in the electrolyte should be of insulating material. If metal isv used, it must be coated with insulating material. For etching copper, it is desirable to have a cathode of steel or iron.

Reference will rst be made to Figures 1 and 2. The cathode 38 is a perforated plate extend- 5 ing across the bath at a slight slope to the horizontal. The anode 3 is arranged at the same slope and at an appropriate distance above the cathode.

Electrical connection is made with the plate 3 by the contact member 9, which consists of a disc I0, of the same metal as the plate 3, and a casing of insulating material Il, serving as a holder for the disc I0 and the end of the flexible connecting cable |2. The disc I0 is recessed in the centre part of the lower face. Effective contact is secured by the weight of the contact member. No mechanical connection is made between the contact and the plate, so that the member 9 can readily be lifted away from the plate and replaced as required in the manipulation of the plate during the process of etching.

Below the cathode is arranged a perforated cylinder 39 made of insulating material and having at each end an impeller 23, communicating in the end discs 22. The upper ends of these impellers 23 work in chambers shut off from the main part of the tank by partitions 24. The cylinder 39 is mounted on a shaft 4 by means of the end discs 22. The impellers 23 are also mounted on the shaft 4 and the shaft is carried in bearings in housings I5 and projects at the right hand end where it is driven through the pulley Il mounted on it. The action of the impellers 23 due to the rotation of the shaft is to draw in through the perforations in the cylinder 39 a stream of electrolyte and carry it through holes in the end discs 22 into the impellers and then discharge thrI ugh the holes in the periphery of the im- 40 pellers. The enclosure of the upper parts of the impellers by the partitions 24 prevents undue disturbance of the surface of the bath and ensures a thorough circulation of the electrolyte. The

partitions 24 extend down to the level of the 45 cathode 38. Below the agitator, near the bottom of the tank, is placed a perforated sheet 40 of insulating material. This serves as a screen below which is collected the finely divided metal which is etched from the anode and precipitated in the electrolyte. This material falls through the perforations in the screen 40 and is protected from the disturbing influence of the agitator and accordingly remains below the screen. From this place, it can be removed from time to time, when a large quantity has collected.

In using barriers to control the current distribution on the anode, it is the function of the barrier arrangement to render ineffective the whole of the surface of the cathode except that lying below the anode and having an area less than the anode owing to the masking of a strip along each of the four sides.

In the arrangement shown in Figures 1 and 2, two of the barriers are formed by supports 4| and 35 42, arranged respectively along one longitudinal side and one end of the main part of the tank. These barriers also serve as supports for the anode, being provided for this purpose with ledges 43 and 44. One of the other barriers is 70 pr0vided`by a transverse member 45 which is movable along the bath, being carried at one side on a rod 46 and the other side on the ledge 43 of the barrier 4|. This transverse member 45 is provided with a ledge 41 to serve as a third sup- 75 port for the anode 3. The fourth barrier is prowith the interior of the cylinder 39 through holes vided by a longitudinal frame consisting of horizontal parts 49 and 50 and Vertical end pieces 5I. The part 49 is a plate resting on the perforated cathode 38 and extending to the appropriate distance inward beyond the corresponding edge of the anode. The part 50 slides, at one end, onthe ledge 44 of the barrier 42 and, towards thexother end, worksin a slot 6| in the transverse barriermember 45. The two members 49 and 50 extend thewhole length of the cathode and are joined by the\pieces 5|. The member 50 is provided on one edgeYwi-th a rubber cushion 52 which-has a recess to receive the edge of the anode` plate 3. When preparing\\the machine for etching a' plate, thesliding members 45 and 50 are moved up to the correct positions to engage the plate which then rests on the. ledges 43, 44 and 41 and is in close contact with the rubber cushion 52. The object of providing this cushion is to ensure effective contact with the plate at this edge and thus avoid the passage of bubbles of gas round the edge of the plate, which would result in irregular etching at or near the edge.

Slots 8| and 62 are provided to accommodate the members 50 and 49 where they pass through the transverse member 45. For the slot 6|, a cover 63 is provided. This cover 63 has an opening tting the part 50, which slides freely through it in endwise movement but carries the cover 63 with it when it slides along the slot 6I. The cover 63 is kept in contact with the face of the transverse member adjacent to the slot 6| `by the tongue 64 which works in a groove in the projecting outer part 65 of the transverse member. The

Aslot 6| and the cover 63 are made of such dimensions that, when the member 5D has been moved outwards to accommodate the largest size of plate, the cover 63 just closes that part of the slot 6I which is adjacent to the plate. By this means, access of current through the electrolyte to the back of the plate by Way of the slot 6| is prevented.

It will be seen that'the barriers 4| and 42 and the transverse member 45 enclose the space between the anode and the cathode on three sides. The fourth side is left open between the horizontal members 49 and 50. This permits of the flow of electrolyte through this space between anode and cathode. The electrolyte enters between the members 50 and 49, passes down through the perforations in the cathode 38 and enters the perforated cylinder 39 and is driven out through the impellers 23 into the end parts of the tank from which it finds its way back in the course of circulation. No strong current in the space between anode and cathode is necessary. It is only necessary that the flow should suffice to prevent the attainment of any substantial difference of temperature or concentration of the electrolyte-at this part as compared with other parts and to remove bubbles of gas or particles of metal which may be liberated there.

The inwardly projecting parts of the barriers A4|, 42 and the lower part of the transverse member 45 and the inner edge of the member 49 have the effect of screening the cathode so that the area of it directly under the outer edges of the plate is not effective. Owing to the necessity for leaving an open passage between the membersl 50 and 49, it is possible that the outer part of the cathode lying beyond the member 49 might become effective, in some cases, so as to produce excessive etching on the edge of the anode plate vnear to the rubber strip 52. To prevent this possibility, the outer edge of the member 49 may be provided with a flexible extension formed of insulating material, such as a sheet of rubber,

which covers the-part of the cathode between the member 49 and the higher edge of the cathode. Such a flexible extension is shown in Figures 1 and 2 as a sheet 53 attached to the rear edge of the member 49 and to an anchor strip 54 and hanging downward in a loop between the higher vedge of the cathode 38 and this anchor strip. This arrangement permits the member 49 to be moved over the cathode to the extent required to accommodate the different sizes of plates to be dealt with while securing effective shielding of the anode from the portion of the latter. i f

It will be seen that, with the arrangement lllustrated in Figures 1 and 2, it is necessary for the plate to be placed always in one corner-of the tank. This may be inconvenient when workv ing with small plates where a more central position may he a convenience for the operator.

To avoid this necessity of working in one corner of the tank, an arrangement, as shown in Fig- 'ures 3 and 4, may be .employ/ed. In this, two

transverse members similar 4to the part 4.5 shown in Figure 1 are used. These areV indicated by 55 and 56. Their lower parts project inwardly and form barriers 51 and 58. Above these barriers are provided ledges 59 and 60 'on 'which the plate rests. 'Ihese two sliding members cooperate with the fixed barrier member 4I having a ledge 43 for the support of the plate. This barrier 4I is attached to the side of the tank in the position shown in Figure 2. The 'two sliding members 55 and 56 are supported at one end on this ledge V43 and'at the other end of the rod 46. They can accordingly be moved to any positions along the tank and can accommodate the required range of plates between them. A plate 3 is shown in position in Figure 4. The fourth barrier is provided by a frame which is similar to that formed by the parts 49, and 5| in Figures 1 and 2 with the exception that the two upright members 5l are at the extreme ends of the frame in the arrangement shown in Figures 3 and 4. A rubber cushion 52 is placed along the inner face of the member 50 in this arrangement as in that shown in Figures 1 and 2.'

As in the arrangement shown in Figures 1 and 2, a slot 6I with a cover 63 is provided in each of the transverse members and 56 for the member 50 and corresponding slots 62 for the member 49. Each of the covers 63 is slidably connected to its associated transverse'member by a tongue-and-groove connection 63a.

An alternative form of machine is shown in Figures 5 and 6. In this example, one of the barriers is provided by a flexible sheet in the form of a continuous band movable on a pair of rollers and the other is a vertical strip extending the full width of the cathode and movable at right angles to the edge ci the first barier.

In this example, the whole of the machine is mounted on a frame made of hard wood, which is placed within but not connected with the tank I so that the contents may be lifted completely grid 10. This is a perforated plate of insulat- It may, for instance, be made of porceing material which lies on the upper face of the cathode and'ls capable of sliding backwards f and forwards on this surface, being actuated by the lever 1|, pivoted at 12 on one of the planks 61.

is only necessary to move the`grid at intervals By this reciprocatory movement, the grid can clear the upper faceof the cathode of deposits of loose metal or other substances. It

so as toprevent the deposit becoming excessive. i

Near each end of the planks 61, are mounted, in bearings in the planks, two roller's 13, round which passes an endless band of rubber 14, the

upper part of which lies upon the grid 10. The

movement of the band is brought about by means of the worm and worm wheel, shown as acting upon the right roller in Figure 5 and actuated by a handle 15 on a vertical spindle. The ,band 14 consists of two substantially equal parts. 'One of these, (shown in the left hand part of Figure 5) extends the full width of the cathode forming a continuous cover for that part of the cathode over which it lies. The other part of vthe band consists of two narrow strips, one at each side. These cover only the extreme edges of the cathode. At the upper end of the full portion of the band is located a stiiening strip 16 which may be of hard rubber, and, immediately behind this str-ip and near one side of the band, is mounted on the band a vertical peg 11. f

Between the planks 61 extends a transverse member 18 which lies near the right hand end of the cathode in Figure 5 and has an inclined projection 19 `with a ledge at the upper end of it. On this ledge rests one edge of the plate 3 to be etched. The projection 19 serves as a barrier and covers a strip of the cathode to the required extent. The upper part of the transverse members 18, which extends above the level 2 of the electrolyte, shields the adjacent edge and back part ofthe plate from' the current. At the opposite edge, the barrier is provided by the band 14 and its stiffening strip 16. This band is adjusted by the handle 15 until the peg 11 comesv upper edge a ledge for the plate to rest on. On

the other side is a movable barrier 8| which also has a projecting lower edge and a ledge to receive the plate. This barrier slides across the cathode, being carried at one end on the rod 62 and at the other end on the ledge on the barrier 19. I

No means for agltating the electrolyte is shown in Figures 5 and 6. It can, however, be provided if necessary, 4either in the lower part or at the ends of the tank. The use of the scraper grid 10 takes the place of a separate agitator to-some In the alternative form of apparatus shown in Figures 7, 8 and 9 provision is made for supporting the anode plate 3 on two or three sides only. Referring to these gures the contact member consists of a block 83 of the same metal as the plate 3 mounted on a rod 84, serving also to connect the block 83 with the end of a flexible connecting cable 85. When not in .use the contact member is supported on a hook 88. Effective contact is secured by the weight of the contact member, no mechanical connection being made between the block 83'and the plate 3 so that the contact member can readily be lifted away from the plate and replaced as required in the manipulation of the plates during l5 the process of etching.

The cathode 81 consists of a perforated plate which is so supported as to slope to the horizontal to a slight extent, (about one in fteen). The cathode is mounted on a frame made of 20 hard Wood as in the previous construction described. The principal members of'the frame are four vertical posts 88 connected by transverse members 9| and carrying ebonite sheets 89 and 90 at their upper ends. A member 93 for 25 supporting the plate 3 is removably mounted against the end sheet 90 adjacent to the lower edge of the cathode 92, and similar members 94 are mounted against the side sheets 89 the lower .edge 92 of the cathode is spaced from the mem- 30 ber 93 by a distance equal to about one-quarter to one-half the distance between .the anode and the cathode. Members 94 carry blocks 95 at their lower edges which act as masks for the cathode 81. The plate issupported on an third 35 side by a cross-member consisting of an ebonite sheet 96 supported vertically on a base 91. The sheet 96 is apertured at 98 and a member 99 extends along the upper edge of the aperture 98 and projects therefrom on both sides tot pro- 40 vide ledges for. supporting anode plates. The

cross-member may bemoved from side to side.

along the tank, so that ,different sized plates may be treated. The sheet 96 is provided with a rectangular notch which engages with a bead- 45 ing |00 on the upper of the side sheets 90. The base 91 of the cross-member acts as a mask to cover a strip of the cathode opposite to one edge of the plate 3. It will be seen that the effective area of the cathode, if projected, would lie with- 50 ln the boundary of the plate, by an approximately constant distance on three sides, by virtue of the masking effect of the member 91, one of the blocks 95 and the space between Athe lower edge 92 of the cathode and the side sheet 90.

55 Every time the plate 3 is removed from the bath for treatment it is turned in its own plane before being'replaced so`that a different edge is exposed to the cathode.

In this construction more than one plate may 50 be treated at once and -forA this purpose twol contact members are provided and an additional cross-member. In Figure 9 a plate I0| is shown in position supported and masked on one side by the cross-member used for supporting 05 the plate 3 and on the other side by a similar cross-member |02. The plate-10| will need to be turned more frequently than th'eplate 3 inorder to obtain even etching since two of its edges are to the pipes |03 through pipes |05 and the supply is controlled by a valve |06.

It will generally be advantageous to make of rubber each of the faces of the barriers and side planks on which an edge of the anode plate 5 rests in the constructions, described, so as to provide a yielding support ensuring good contact between the plate and the carrier and preventing the lodging of bubbles of gas or particles of solid material there. 10

What we claim as our invention is:

1. Electrolytic etching apparatus comprising a bath, a fiat cathode in said bath, means for supporting a flat anode to be etched in said bath inparallel relation to said cathode and supporting means comprising a fixed Wall on each of two adjacent sides, extending between the cathode and anode and projecting inwardly at the cathode to make the effective area thereof less than that of the anode by a strip on each of the two sides, and an adjustable supporting member on at least' one of the other two sides, said member being located in position by the anode and masking a strip of the cathode.

2. Electrolytic etching apparatus comprising a bath, a flat cathode in said bath, means for supporting a flat anode to be etched in said bath, in parallel relation to said cathode and making the effective area of the cathode less than the area of the anode, said means comprising a fixed wall on one side extending between the cathode and anode and projecting inwardly atthe cathode to make the effective area thereof less` than the anode by a strip, movable walls on two opposite sides of the anode and a movable strip on the fourth thereof, each of these three movable members being located in position by the anode and masking a strip of the cathode.

3. Electrolytic etching apparatus comprising a bath, a at cathode in said bath, means for supporting a flat anode to be etched in said bath in parallel relation to said cathode, said means comprising a xed wall on at least one s ide extending between the, cathode and anode and projecting inwardly at the cathode to makethe effective area thereof less than that of the anode by a strip on the said side, and an adjustable member on at least one other side, the said member or members being located in position by the anode and masking a strip of the cathode.

, 4. Electrolytic etching apparatus comprising a bath, a flat cathode in said bath, means for supporting a fiat anode to be etched in said bath in parallel relation to said cathode, said means comprising fixed walls on two adjacent sides vextending between the cathode and anode, one of said walls projecting inwardly at the cathode and the cathode being spaced inwardly from the other said wall to make the effective area of the cathode less than that of the anode by'a 60 strip on said two sides and an adjustable member on at least one of the other sides, said adjustable member or members being located in position bythe anode and masking a strip of the cathode. 65 5. Electrolytic etching apparatus comprising a bath, a fiat cathode in the bath, means for supporting a flat anode to be etched in said bath in parallel relation to said cathode, said means comprising a fixed wall on at least one side extending between the cathode and anode, the cathode being spaced inwardly from the said wall to make the effective area of the cathode less than-that of the anode by a strip on said side and an adjustable member on at least one of -the cathode on said other side.

6. Electrolytic etching apparatus comprising a bath, a flat cathode in said bath, means for supporting a flat anode, to be etched in said bath, in parallel relation to said cathode and means for masking an edge part of the cathode and making the effective area thereof less than that of the anode, said masking means comprising a flexible sheet of insulating material and means for moving it over the surface of the cathode and means for determining the position of the -edge of said sheet in dependence on the size of the anode so that the edge of the sheet is adjusted into a position in advance inwardly of the edge of the anode.

'7. Electrolytic etching apparatus comprising a bath, a flat rectangular cathode in said bath, adjustable 'means for supporting a fiat rectangular anode, to be etched in said bath, in parallel relation to' the exposed surface of said cathode and making the eiective area of the cathode less than the effective area of the anode,y said means comprising a fixed wall on one side extending between the cathode and anode and projecting inwardly at the cathode, to make the effective area thereof less than the effective area of the anode by a strip, movable walls on two opposite sides of the anode and a movable strip on thefourth side, each of these three movable members being located in position by the anode and masking a strip of the cathode whereby the effective area of the cathode is less than the effective area of the anode.

8. Electrolytic etching apparatus comprising a bath, a at cathode in said bath, means for supporting-a at rectangular anode to be etched in said bath in parallel relation to said cathode, consisting of supports for at least two sides thereof, a member adapted to bear against an edge of the anode, means covering the cathode and movable in a direction parallel to said cathode for varying the eective area thereof, said covering means being operatively connected with said member with the leading edge of the 'covering means sufciently in advance thereof towards the centre of the effective part of the cathode to maintain the effective area ofthe cathode less than the exposed area of the anode by a strip having a predetermined width, said covering means being limited in movement parallel to the cathode by said member coming to bear against the anode.

9. Electrolytic etching apparatus comprising a bath, a fiat cathode in said bath,'means for supporting a fiat rectangular anode to be etched in said bath in parallel relation to said cathode, consisting of supports for at least two sides thereof, a member adapted to bear against an edge of the anode, covering means movable in `a direction parallel to said cathode for varying the effective area thereof, said covering means comprising a exible sheet of insulating material which rests on the surface of said cathode and being operatively connected with said member so that -the leading edge of the covering means moves in advance thereof towards the centre of the effective part of the cathode, being limited in movementpa'rallel to the cathode by said member coming to bearA against the anode, whereby to make the effective area of the cathode less than the exposed area of the anode by a strip having a predetermined width.

10. Electrolytic etching apparatus comprising a bath, a iiat cathode in said bath, means for supporting a flat anode to be etched in said bath in parallel relation to said cathode, said means comprising a wall at each of two4 sides extending between the cathodegand anode an'd projecting inwardly at the lcathode to form aby a strip of predetermined Width on each of the two sides, at least one of said walls beingladjustable in position over the cathode and being located in position by the anode.

4 FRANCIS JOSEPH BRISLEE.

REGINALD BLACKBURN. 

